(1) Field of the Invention
The present invention relates to a method of bending straight pipe sections into pipe elbows and to an apparatus for performing this bending operation.
(2) Prior Art
Basically, two processes are currently used for making pipe elbows: the bending method and the welding method. In the bending process, a straight piece of pipe is clamped in a vise and formed into a bend after having been filled with a suitable filler and tightly sealed at both ends. This process has several disadvantages such as the high costs of a bending machine, the great forces which are to be used and the reduction in the wall strength of the pipe elbow at the outer curve of the bend. It is specifically this reduction in strength which adversely influences the load containing capacity of the entire pipe elbow and forces the manufacturer to select a far thicker pipe wall for the application than is actually required; as a result, much higher material costs are accepted simply to ensure that the critical outer wall of the pipe elbow is sufficiently strong at the end when the pipe is bent.
In the welding method, the starting point is a flat piece of sheet metal large enough to correspond to the development of the entire pipe elbow to be made. This piece of sheet metal is then suitably rolled up to form the shape of the pipe elbow and welded together. There are two main disadvantages: First, a significant part of the sheet metal is lost as waste and second, a significant mechanical effort is required for cutting, rollforming and welding the pipe elbow. Also, these are time consuming tasks.